Expediting the purchase of new imaging devices.
Explore the source record for details and available documents.
Diagnostic Imaging↗
Biomedical subjects
G D Fullerton
Publications and source records attributed to G D Fullerton.
Evidence that a major portion of cellular potassium is "bound".
In this report we briefly review recent evidence which shows that a substantial proportion of intracellular K+ is "bound" or perturbed from the physicochemical properties expected in dilute aqueous solutions. In addition, we present evidence from electron probe x-ray microanalysis of thin cryosections of cells which indicates that the binding of K+ to anionic groups either carboxyl groups (HCO2) on proteins or to phosphate groups in creatine phosphate (CrP), in adenosine triphosphate, (ATP), in protein and in nucleic acids, are the main determinants of the maintenance of (as differentiated from the generated of) the well known intra- to extracellular K+ concentration difference. The collective evidence suggests that much of cellular K+ is reduced in its mobility and in its chemical activity due to association with negative charge groups (e.g. carboxyl and phosphates). This fact forces abandonment of the misleading assumption that the majority of intracellular K+ and other inorganic ions are as free as would be expected under ideal solution conditions. This realization should have far reaching consequences toward understanding transmembrane movement of water and solutes in cells.
Animals↗
Chronically obstructed sinonasal secretions: observations on T1 and T2 shortening.
Clinically assessed chronic proteinacious sinonasal secretions usually have long T1 and T2 relaxation times reflecting their high water content. However, in some cases variable combinations of short and long T1 and T2 relaxation times are found. To study the causes of these findings, the magnetic resonance (MR) images of 41 patients with surgically proved, chronically obstructed sinonasal secretions were studied. The relative signal intensities on both T1- and T2-weighted sequences of the sinus specimens were correlated with the gross viscosity of the specimens at surgery. Ten specimens were collected that were not contaminated with either blood or saline. UV spectrophotometric analysis of four of these samples excluded the presence of methemoglobin. Total protein content was determined in five samples, and in vitro T1 and T2 values were measured in one sample. These T1 and T2 relaxation times were accurately predicted with use of a standard pure lysozyme protein solution with the same concentration as the specimen. In addition, the observed T1- and T2-weighted signal intensities on the 41 MR images were predicted from an analysis of pure protein solutions. This study concludes that the primary causes of the variable T1 and T2 relaxation times of chronic sinonasal secretions are the macromolecular protein concentration, the amount of free water, and the specimen viscosity. Furthermore, an orderly and predictable transition of these signal intensities occurs over time.
Chronic Disease↗
Extent and properties of nonbulk "bound" water in crystalline lens cells.
Crystalline lenses provided good material to study and measure the properties of cellular water. Different methods were used to establish the extent and properties of nonbulk water in mammalian lenses. These methods include: NMR titration analysis, a test of the osmotic properties, a test of dye exclusion In lenses with intact cell membranes and in lenses with disrupted cell membranes, and the water-holding capacity of lenses subjected to 40,000 x g for 1 hour with intact cell membranes and in lenses with disrupted cell membranes. The data from these methods, as well as other data from the literature, lead to the conclusion that most, if not all, of the water in lens cells (up to 2.2 g water/g dry mass) has motional and osmotic properties that distinguish it from bulk water. These findings call into question the common and convenient assumption that all but a small proportion of cellular water is like that in dilute solution.
Animals↗
Water of hydration in the intra- and extra-cellular environment of human erythrocytes.
The proton nuclear magnetic resonance (NMR) titration method (which requires measurement of the relaxation rate at multiple measured levels of dehydration) was applied to the analysis of human erythrocytes, a hemoglobin solution, plasma, and serum. The results allowed identification of bulk water and four motionally perturbed water of hydration subfractions. Based on previous NMR studies of homopolypeptides we designated these subfractions as superbound, irrotationally bound, rotationally bound, and structured. The total water of hydration (sum of both structured and bound water subfractions) in plasma, serum, and hemoglobin ranged from 2.78 to 3.77 g H2O/g dry mass and the sum of the three bound water subfractions ranged from 1.23 to 1.72 g H2O/g dry mass. The total water of hydration on hemoglobin, as determined by (i) spin-lattice (T1) and spin-spin (T2) NMR data, (ii) quench ice-crystal imprint size, (iii) calculations based on osmotic pressure data, and (iv) two other methods, ranged from 2.26 to 3.45 g H2O/g dry mass. In contrast, the estimates of total water of hydration in the intact erythrocytes ranged from 0.34 to 1.44 g H2O/g dry mass, as determined by osmotic activity and spin-lattice titration, respectively. Studies on the magnetic-field dependence of the spin-lattice relaxation rate (1/T1 rho) of solvent water nuclei in protein solutions and in intact and disrupted erythrocytes indicated that hemoglobin aggregation exists in the intact erythrocytes and that erythrocyte disruption decreases the extent of hemoglobin aggregation. Together, the present and past data indicate that the extent of water of hydration associated with hemoglobin depends on the amount of salt present and the degree of aggregation of the hemoglobin molecules.
Body Water↗
Influence of cytomatrix proteins on water and on ions in cells.
This review concerns the influence that cytomatrix proteins have on the motional properties of water and on the major inorganic ions in cells. The techniques we used for study of water in cells and on the cytomatrix proteins include: pulsed NMR of water protons, quench cooled ice crystal imprint size, and osmotic behavior. The technique for study of ions involved use of electron-probe X-ray microanalysis of thin cryosections of cells. The cytomatrix was found to play the major role in determining the extent of hydration water in cells. The amount of hydration water varied greatly between cell types (e.g., lens fiber cells have no detectable bulk water) and varied in the same cell type studied under different states (e.g., unfertilized and fertilized sea urchin eggs). Aggregation of cytomatrix proteins (actin in particular) is a determinant of the extent of hydration water in cells. Hydration water appears not to participate in the ideal osmotic equation of van't Hoff. The ionic content of cells does not accurately predict the chemical activity of the ions in cytoplasm. A major proportion of intracellular K+ and a substantial fraction of Cl- was found to be influenced by the cytomatrix such that their diffusion was impaired. The cytomatrix is responsible for the decreased motional properties of a substantial portion of cellular water and ions.
Animals↗
Quench cooled ice crystal imprint size: a micro-method for study of macromolecular hydration.
Quench cooling (rate greater than 4000 degrees C/sec) of biological specimens limits growth of ice crystals by processes different from slow cooling methods. Quench cooling in liquid propane cooled in liquid nitrogen induced ice crystal segregation compartments, as imaged by scanning transmission electron micrographs of freeze-dried cryosections of tissues and protein solutions. The observed imprints of ice crystals were relatively small and roughly spherical. The size of these ice crystal imprints increased with distance from the specimen/quenchant surface. Beyond a depth of 150 microns the size of the imprints was constant but differed among subcellular compartments. The size of the imprints was found to be dependent on: water content, extent of hydration water and the degree of protein aggregation. Determination of extent of hydration water and degree of protein aggregation in protein solutions by measurements on the size of ice crystal imprints yields data in agreement with macroscopic methods. Thus ice crystal imprints give information about the interactions of macromolecules and water at a subcellular level of resolution.
Animals↗
Cell cycle changes in water properties in sea urchin eggs.
This study concerned changes in the motional properties of cellular water during the first cell cycle of fertilized sea urchin eggs (Lytechinus variegatus). There was a significant decrease in proton NMR T1 relaxation time and in cytoplasmic ice crystal growth during mitosis and a significant increase in T1 time and cytoplasmic ice crystal size during cleavage. This was not caused by egg water content changes as reflected by egg volume measurements. Removal of both the fertilization membrane and the hyaline layer shortly after fertilization did not alter the pattern of T1 time changes at mitosis and cleavage as compared to whole eggs; thus, the pattern of T1 time changes was attributed to intracellular events. Treatment of fertilized eggs with cytochalasin B, an inhibitor of actin polymerization, did not block the fall in T1 time at mitosis, but did block cytokinesis and the increase in T1 time, which normally occurred at cleavage. A significant pattern of actin disassembly and reassembly at mitosis and cytokinesis was found by studies on the total amount of monomeric actin (G actin) using the DNase I assay. This led to the hypothesis that the observed changes in T1 time and ice crystal size during the first cell cycle were due to the depolymerization and polymerization of cytoplasmic actin. To test this, the effect of the in vitro polymerization of purified actin on the T1 time and on ice crystal growth was examined. It was concluded that changes in the T1 time and ice crystal growth upon polymerization of actin in vitro resembled the changes seen in vivo. These results suggest that changes in the motional properties of cytoplasmic water during the first cell cycle are due, at least in part, to the state of polymerization of cytoplasmic actin.
Actins↗
Effects of cytoskeletal inhibitors on water proton relaxation time changes in unfertilized and fertilized sea urchin eggs.
Unfertilized and fertilized sea urchin eggs were used for pulsed proton NMR spin-lattice relaxation time (T1) measurements of cellular water. An 81% increase in T1 time at fertilization was largely explained by the accumulation of extracellular water in the perivitelline space. To assess the role of microtubule and actin filament assembly and disassembly, eggs were treated with drugs that are known to change these cytoskeletal elements (i.e., colchicine, taxol and cytochalasin B). Egg volume was also monitored in all studies to rule out the influence of water content changes on the observed T1 relaxation time changes. Neither assembly nor disassembly of microtubules changed the T1 relaxation time. The role of actin polymerization and depolymerization is discussed as a possible explanation for the observed cell cycle dependent water proton T1 relaxation time changes.
Actins↗
The influence of macromolecular polymerization of spin-lattice relaxation of aqueous solutions.
The docking or polymerization of globular proteins is demonstrated to cause changes in proton NMR spin-lattice (T1) relaxation times. Studies on solutions of lysozyme, bovine serum albumin, actin, and tubulin are used to demonstrate that two mechanisms account for the observed changes in T1. Polymerization displaces the hydration water sheath surrounding globular proteins in solution that causes an increase in T1. Polymerization also slows the average tumbling rate of the proteins, which typically causes a contrary decrease in T1. The crystallization reaction of lysozyme in sodium chloride solution further demonstrates that the "effective" molecular weight can either decrease or increase T1 depending on how much the protein is slowed. The displacement of hydration water increases T1 because it speeds up the mean motional state of water in the solution. Macromolecular docking typically decreases T1 because it slows the mean motional state of the solute molecules. Cross-relaxation between the proteins and bound water provides the mechanism that allows macromolecular motion to influence the relaxation rate of the solvent. Fast chemical exchange between bound, structured, and bulk water accounts for monoexponential spin-lattice relaxation. Thus the spin-lattice relaxation rate of water in protein solutions is a complex reflection of the motional properties of all the molecules present containing proton magnetic dipoles. It is expected, as a result, that the characteristic relaxation times of tissues will reflect the influence of polymerization changes related to cellular activities.
Actins↗
Magnetic resonance imaging signal concepts.
Explore the source record for details and available documents.
Humans↗
An evaluation of the hydration of lysozyme by an NMR titration method.
In this study a new titration method is proposed to study the motional properties of water molecules in conjunction with globular proteins using proton NMR relaxation measurements. The method was applied to the study of the interaction of water with lysozyme and allowed identification of four water fractions-superbound water, polar-bound water, structured water and bulk water - in exchanged equilibrium. The titration demonstrated that 193 water molecules are hydrogen bonded directly to the lysozyme molecule. The combination of structured and bound water extends to 1.4 g H2O per g lysozyme and approx. two to three layers from the surface of the macromolecule. It is proposed that this structured water is related to non-isotropic water rotation in conjunction with hydrophobic patches and directly related to 'hydrophobic bonding' changes. Water amounts greater than 1.4 g H2O per g lysozyme are sufficiently distant from the macromolecule for motion to revert to that typical of water in bulk. The typical correlation times for water motion in the four fraction are: over 10(-6) s (superbound); 10(-9) s (polar bound); 10(-11) s (structured) and 10(-12) s (bulk). These results correlate well with results from other measurement techniques found in the literature.
Chemical Phenomena↗
Characterization of water in unfertilized and fertilized sea urchin eggs.
The water in unfertilized and fertilized sea urchin eggs was characterized with a proton nuclear magnetic resonance (NMR) titration method assuming fast proton diffusion (FPD) between water compartments. This method involves stepwise dehydration with sequential T1 relaxation time and water content determinations. The results analyzed by the FPD model give evidence of intracellular water compartments with three different correlation times: 6 X 10(-12) sec (bulk water), 1 X 10(-10) sec (structured water) and about 2 X 10(-9) sec (bound water). Fertilization is accompanied by a substantial increase in bulk water (from 111 to 414 g H2O per 100 g dry mass) and by a decrease in the water of hydration (from 128 g to 56 g per 100 g dry mass). This study shows that 54% of the water in the unfertilized sea urchin egg has motional properties different from bulk water and that this percentage decreases dramatically shortly after fertilization. Most of the change in T1 relaxation rate observed at fertilization can be accounted for by uptake of bulk water associated with elevation of the fertilization membrane.
Animals↗
Molecular masking and unmasking of the paramagnetic effect of iron on the proton spin-lattice (T1) relaxation time in blood and blood clots.
The contribution of hemolysis, proteolysis and the paramagnetic effect of iron on the proton spin-lattice (T1) relaxation time in blood was examined. Hemolysis induced by sonication resulted in a significant (10%) increase in the T1 relaxation time of whole blood. Proteolysis in both sonicated and unsonicated whole blood samples eventually yielded T1 values which correlated well with the relaxation times of free iron in plasma or water at concentrations comparable to the concentration of iron in whole blood. It is concluded that proteolysis allows the iron atom to express its paramagnetic effect on water relaxation by gradually destroying the hydrophobic nature of the pocket in which iron resides on the hemoglobin molecule. The contribution of various blood components to the T1 relaxation of whole blood was also studied. The T1 values for packed erythrocytes, intact whole blood, sonicated whole blood, plasma and serum proved to be significantly different from each other. Serum was found to have a significantly (12%) longer T1 relaxation time than plasma. Packed clotted blood in vitro showed no change in the T1 time for at least 13 days while packed erythrocytes showed a shortening of T1 time after 6-8 days.
Blood↗
Orientation of tendons in the magnetic field and its effect on T2 relaxation times.
In vitro studies of spin-spin relaxation times of the protons or hydrogen nuclei which make up the tendon demonstrated significant dependence of T2 on orientation at physiological levels of hydration. T2 varied from approximately 250 mu sec. with the tendon aligned with the magnetic field to 22 msec. at an angle of 55 degrees or 125 degrees and 4 msec. at deviations of +/- 15 degrees from 55 degrees and 125 degrees. 55 degrees and 125 degrees are the so-called "magic angles" at which 3 cos2 theta - 1 = 0. As a result, the signal from human tendons in vivo will depend on their orientation; however, T2 is generally short enough that the signal intensity will approach 0 in MR images regardless of the orientation of the tendons, thereby preventing this phenomenon from being observed in most studies.
Animals↗
Proton magnetic resonance relaxation behavior of whole muscle with fatty inclusions.
This in vitro proton study of spin lattice (T1) and spin spin (T2) relaxation of muscle with storage-fat inclusions demonstrates slow exchange and lack of cross-relaxation between fat and water. Slow exchange causes biphasic T1 relaxation, but T2 relaxation is paradoxically uniphasic due to the nearly equal T2 values for both fractions. By careful dehydration and fat extraction, the relaxation information was deconvolved into water, fat, and protein contributions. The biphasic T1 decay has a short component due to lipid and a long component due to the water-protein combination. The fat content of muscle can be measured from the relative amplitude of the two T1 components or directly from the T2 relaxation time.
Adipose Tissue↗
Water ordering during the cell cycle: nuclear magnetic resonance studies of the sea-urchin egg.
Nuclear magnetic resonance was used to measure spin-lattice water proton relaxation times (T1) during the first cell cycle in sea-urchin zygotes of packed Strongylocentrotus purpuratus. Following insemination there was a 90% increase in the T1 value. The increase in T1 at fertilization could be accounted for by the accumulation of extracellular fluid between the egg surface and the fertilization envelope. The T1 value then remained without change during the first cell cycle, except at metaphase when there was a significant 13% decrease. The lowered T1 values measured at metaphase were not related to a change in the water content of the packed cells, which remained fairly constant throughout the cell cycle. High hydrostatic pressure, low temperature and colchicine (agents that depolymerize mitotic apparatus microtubules) did not affect the T1 values in fertilized eggs. Treatment in vitro of a microtubule protein preparation with low temperature and colchicine resulted in an increased T1, which accompanied the depolymerization of microtubule protein. Since depolymerization of the microtubules associated with the mitotic apparatus by high pressure, colchicine or low temperature does not alter the T1 of water protons in the cell, it is proposed that the increased state of ordered water molecules at metaphase is maintained by nonmicrotubular factor(s) of the metaphase egg.
Animals↗
Relationships between ice crystal size, water content and proton NMR relaxation times in cells.
Biological specimens were frozen under controlled conditions. We questioned how the size of ice crystals, as measured in cryosectioned and cryoadsorbed sections of these biological specimens, relates to the water content and to the proton NMR relaxation times (T1 and T2) of the unfrozen specimens. The results permit the following conclusions: After rapid freezing in liquid propane cooled in a liquid nitrogen bath, the average size of ice crystals at distances of 150 microns or more from the surface of a particular tissue was always the same. Thus, the average size of the ice crystals was found to be characteristic of the type of biological tissue studied. Linear regression analysis showed average ice crystal size to have a significant correlation coefficient to T1 relaxation time and to water content. Specifically ice crystal size increased with T1 relaxation time and with water content. Multiple regression and path analysis demonstrated a positive correlation between the T1 relaxation time and the ice crystal size variation. Path analysis showed that both water content and T2 relaxation time were less directly correlated with ice crystal size. The findings from the path analysis and other observations show that the average size of ice crystals in subcellular compartments is best predicted by the proton T1 relaxation time. A working model is put forth to explain differences in ice crystal size observed between specimens enriched in globular or in parallel filamentous proteins.
Animals↗